[Bug 2078555] Re: Upgrading from 22.04 to 24.04.01 breaks dnsmasq

[Nick Rosbrook]

** Changed in: ubuntu-release-upgrader (Ubuntu Noble)
    Milestone: None => ubuntu-24.04.2

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https://bugs.launchpad.net/bugs/2078555

Title:
  Upgrading from 22.04 to 24.04.01 breaks dnsmasq

Status in Ubuntu:
  Triaged
Status in dnsmasq package in Ubuntu:
  Invalid
Status in systemd package in Ubuntu:
  Invalid
Status in ubuntu-release-upgrader package in Ubuntu:
  Invalid
Status in The Jammy Jellyfish:
  New
Status in dnsmasq source package in Jammy:
  Invalid
Status in systemd source package in Jammy:
  In Progress
Status in ubuntu-release-upgrader source package in Jammy:
  Invalid
Status in The Noble Numbat:
  New
Status in dnsmasq source package in Noble:
  Invalid
Status in systemd source package in Noble:
  Won't Fix
Status in ubuntu-release-upgrader source package in Noble:
  In Progress

Bug description:
  [Impact]

  During upgrades, systemd-resolved will be started and enabled, even if it was not previously. This is due to (a) the package split that made systemd-resolved its own package (during kinetic cycle, hence between jammy and noble), and (b)
  an ubuntu-release-upgrader quirk that (re)starts systemd-resolved out of stub
  mode during the upgrade to avoid DNS resolution failures during the upgrade.

  [Test Plan]

  The complete test plan requires the fixed version of systemd *and*
  ubuntu-release-upgrader.

  On a Jammy machine, install systemd from jammy-proposed:

  $ cat > /etc/apt/sources.list.d/proposed.list << EOF
  deb http://archive.ubuntu.com/ubuntu/ jammy-proposed main universe
  EOF
  $ cat <<EOF >/etc/apt/preferences.d/proposed-updates
  Package: *
  Pin: release a=jammy-proposed
  Pin-Priority: 400
  EOF
  $ apt update && apt install -y -t jammy-proposed systemd
  $ apt policy systemd

  Then, disable systemd-resolved, and install dnsmasq:

  $ systemctl disable --now systemd-resolved
  $ sed -i 's/nameserver.*/nameserver 1.1.1.1/g' /etc/resolv.conf # Use any DNS server
  $ apt install dnsmasq -y
  $ systemctl status dnsmasq systemd-resolved

  At this point, dnsmasq should be running, and systemd-resolved should
  not. Now, we can run the upgrade:

  $ do-release-upgrade --proposed
  [...]

  The upgrade should complete normally. At the end, systemd-resolved
  should still be disabled/inactive, and dnsmasq should still be
  running:

  $ systemctl status dnsmasq systemd-resolved

  [Where problems could occur]

  systemd:

  The patch is adding a new systemd.prerm. Any issues here would be seen
  during package upgrades of systemd in/from Jammy. It is designed to
  only run during upgrades to Noble from Jammy, so the scope is limited
  there. If something did occur, it would be within the deb-systemd-
  helper script, which would not be fatal to the systemd.prerm script
  given the || true after the invocation.

  ubuntu-release-upgrader:

  The patch adds a call to systemctl is-active to check whether systemd-
  resolved is running. If this was broken, systemd-resolved might be
  started during the ugprade anyways. This would not lead to systemd-
  resolved being enabled, though.

  [Other information]

  For the complete upgrade experience to be fixed for affected users,
  both of these updates need to land. Hence, we should aim to release
  these at the same time. However, having one fix but not the other
  would not make the situation any worse.

  [Original Description]

  Was running Ubuntu 22.04 as home gateway/firewall with dnsmasq as
  dns/dhcp server. Previous upgrade from Ubuntu 20.04 to 22.04 had
  worked without issue.

  After the upgrade to 24.04.01, systemd-resovled was automatically
  enabled. The result was that after a reboot, dnsmasq failed to start,
  as systemd-resolved had already bound to the necessary port. This in
  turn meant that my entire home network lost connectivity as it was
  dependant on dnsmasq running to provide both correct dns and dhcp
  functionality.

  Ideally, during the upgrade process, a check should be made for if
  another dns/dhcp service is already enabled, and if so, not enable
  systemd-resolved.

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